Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002 COMPOSITE TECHNOLOGIES FOR INTELLIGENT INDUSTRIAL LASER PROCESSING prof. VINCENZO PIURI

Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002

COMPOSITE TECHNOLOGIES FOR INTELLIGENT INDUSTRIAL

LASER PROCESSING

prof. VINCENZO PIURIDepartment of Information Technologies, University of Milanvia Bramante 65, 26013 Crema (CR), Italy

prof. VINCENZO PIURIDepartment of Information Technologies, University of Milanvia Bramante 65, 26013 Crema (CR), Italy

EU Project SLAPSSelf-Tuning and User-Independent Laser Material Processing Units

Philips Centre for Industrial Technology


Information SourcesPartners in IMS/Brite-Euram Project

SLAPS• Philips-CFT• Laser Zentrum

Hannover• Odense Steel Shipyard

LTD.• Jurca Opto-elektronik• Fiat-CRF

• Trumpf • Lasag AG• Politecnico di Milano• Ecole Politechnique

Federale de Lausanne - IOA

• University of Vienna

Contributions to the Tutorial: Prof. Cesare Alippi, Politecnico di Milano, ItalyDr. Toon Bloom, Philips CFT, The Netherlands


Laser ProcessingApplying energy to a work piece

in the form of (high intensity) light beam

• Laser seam welding

• Laser cutting

• Laser spot welding

• Laser drilling

• Laser cladding

• Laser marking

• Laser adjustment

• …...


Carbon Dioxide LaserTypical gas laser construction

Discharge power supply

Outputbeam

Gas mixture

Brewster windows

Cavity end mirrors


Nd:YAG Laser

Flash lamp

Nd:YAG rod

Water cooling circuit

Lamp driver

Laser beam outFolding mirror


Solid State Laser Diode

n-type AlGaAs n-type AlGaAsp-type AlGaAs p-type AlGaAsGaAs GaAs

Three layer structure in equilibrium Three layer structure with forward current

EF

EV

EC

-eV-eV

-

++

-EC

EFN

EFP

EV

h


Solid State Laser Diode

• Low output power

• Laser diode arrays for processing

• Low beam quality

• Good control qualities

• High efficiency

P-GaAsP-GaALAsGaAlAs (active layer)N-GaAlASN-GaAs

HEATSINK


Beam Delivery

Cavity

Beam manipulation over multiple (5) axis

Beam expandingand collimating

Translating and rotating mirrors

Focussing mirror

Work piece


Beam Delivery

Cavity Collimatorlens

Work piece

Processmonitoring

Scanningmirrors

Glass fibre delivery

Fibre

F1

F2

Spot size = Fibre core diameter x F1F2


Absorption, Reflection, Transmission

• Kirchhoff: Absorption +reflection+transmission = 1• Extinction of the penetrating light wave

• Penetration depth:fc

c

k oo

o

1

2

1

I(z)

Io

x

xo

kx

ox eIeII

24

)(

1/e


Absorption and Heat Diffusion = F(T)

D a

Temperature

Copper

D a

Temperature

Aluminium

D a

Temperature

Stainless steel


Process Phases

• 1: Heating: Absorption, heat diffusion• 2: Phase transition of top material, change

of properties• 3: Vaporisation, recoil pressure pushes

liquid metal aside• 4: Liquid level reaches bottom and is blown out


Laser Cutting

Laserbeam

Movement

Laserbeam

Top view laser cutting Cross section laser cutting

• Medium to high power CW lasers (CO2)• Process gas, reactive (O2. extra reaction energy)

or not (N2), to blow out molten material• Wave guide kind of energy transfer through

the cutting slit


Spark Pattern During Laser CuttingLaserbeam

Laserbeam

Good qualitycutting

Bad qualitycutting


Process Monitoring

Focussing mirror

AV

2- Impedance measurement

Reactive:Nozzle - work piece distance

Resistive:Plasma detection

1- Optical emission from processing area * Photo diode * spectrometer

Processgas

CCD3- Spreading of sparks

workpiece


Laser Seam Welding

Part A

Part B

Part A

Part B

But-joint Lap joint

Part A

Part B

T-joint


Laser Seam Welding

• Battery casings, Pace maker casings• Car bodies, Transmission parts• Sub assemblies in ship building• Plastics (overlap penetration welding)

Seam weld

KeyholeGap / slit

Movement

Laserbeam

Top view seam welding Cross section seam welding

Undesiredporosity

Laserbeam


Laser Seam WeldingProcess monitoring - Direct delivery system

Focussing mirror

Optical emissionfrom processing area* Photo diode* spectrometer

Processgas

workpiece

Input powermonitoring

2-D thermal imaging


Laser Seam Welding

LaserCollimatorlens

Work piece

Scanningmirrors

Fibre

Temperature

Plumeemission

ReflectedLaser power

Inputlaser power

Process monitoring - Fibre delivery systemSensing implemented in processing head


Overlap fillet

Spot Weld Geometries

Overlap penetration

Nose weld


ProcessMonitoring

in spot welding

200 micronfibre

CCDcamera

Work piece

Laserinput power

Reflectedpower

Plumeemission

Surfacetemperature

Nd:YAG filter

Acousticemission

Eddy currentlosses

X/Y scanningmirror


Signal ProcessingExample of measured signals

Spot welding of 2 x 100 micron copper sheets400 micron spot, 4000 Watt square pulse

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

-1 0 1 2 3 4 5 6 7 8

Time [ms]

Volts

LMO

Plume

Temp lin

Temp log


Signal ProcessingExample of measured signals

Spot welding of 2 x 100 micron copper sheets400 micron spot, 3500 Watt square pulse

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-1 0 1 2 3 4 5 6 7 8

Time [ms]

Volts

LMO

Temp lin

Temp log

Eddy


Automatic Classificationbased on multi sensor process monitoring

• The complete set of sensors provides a broad information range about the performance of the process

• Realisation of data reduction by extraction of specific features from the recorded signals

• The features are recognised as being related to certain process events

• The relations between features and a good or bad performing process have to be established through a large set of verification experiments

Documents

Vincenzo Piuri, SIcon/02, Houston, TX, USA, 18-21 November 2002 COMPOSITE TECHNOLOGIES FOR INTELLIGENT INDUSTRIAL LASER PROCESSING prof. VINCENZO PIURI